The old man does not give his name. He does not say anything at all. Lying under a blanket on a thin mattress in the corner of a dark, prefabricated metal container that these days serves as home, he greets a visitor with a baleful stare. Then, slowly, he turns his face to the wall and pulls his red and black checked keffiyeh over his head.

His misery, shame, anger and isolation seem complete: he is beyond reach. But his tacit statement is both unmistakable and painfully eloquent. Once, not long ago in Syria, he, like so many others, had a family, a house, job, friends, a neighbourhood, a purpose. He was a man in his own right. Life made sense.

Now, inside the confines of the sprawling Zaatari refugee camp a few miles away from the Syrian border in north-west Jordan, he appears as a number, a statistic, his life a shadow of what it was. He seems to be wholly displaced – physically, geographically, socially and psychologically.

Unlike more than 140,000 Syrians who have died since the uprising against Bashar al-Assad's regime began three years ago this week, he is still alive, but for him, at least, the rest could be silence.

Malak and Amjad, aged 27 and 29, and their two small children, Loci, aged two-and-a-half, and Sirin, 20 days old, are also among the 110,000 or so other refugees, most from the same area south of Damascus, at the camp. They do not want their full names published for fear of reprisals against relatives still in Syria.

As Syria's uprising-turned-civil-war enters its fourth year there is little sign of an end to the suffering that has forced 2.5 million people to flee, principally to Jordan, Turkey, Iraq, Lebanon and Egypt. The conflict has internally displaced a further 6.5 million, and left 9.3 million in need of humanitarian assistance, according to UN figures.

More than 180,000 people have simply disappeared, reports the Syrian Observatory for Human Rights. Overall, the total refugee outflow rose more than four-fold in 2013.

"At the beginning there were random attacks and this could be tolerated," Amjad said. "Then [regime forces] started aerial bombing. The buildings were destroyed. Army officers were coming into the village and we were worried for the women. So we decided to leave, though the men mostly stayed behind. It took four days to come across the border, travelling by night. If the army had found us they would have killed us."

Malak, Amjad's wife, said: "We want to go back but it is very difficult. There's nothing left, our neighbours, our families are not there any more. Every day we hear the names of someone who has died or been abducted. My two brothers, my cousin, my uncle all disappeared and we have not heard from them. Another uncle and cousin were killed.

"All the people in Daraa are against the regime … the Americans should have helped our country from the beginning because this is a bloody regime. Everybody is under the direction of the Americans, so nothing happens until America does something … We hope to God we shall return. We don't want to be in the same situation as the Palestinians."

Jordan, in particular, is creaking under the strain as the Geneva peace talks remain at stalemate and the focus of the fighting in Syria appears to shift to a southern front, along the two countries' shared border.

The government estimates that 1.2 million Syrians are now living in Jordan, whose total non-Syrian population is just over six million.

Of the Syrians in Jordan 80% live in the community rather than in the four camps in use. Such is the pressure on resources, a newly constructed camp, at Azraq, with capacity for 100,000-plus, is due to open soon.

"Tensions between Jordanians and Syrians are rising," said Brigadier Waddah al-Hmoud, a Jordanian responsible for security at the refugee camps. "It is not too bad now but we are afraid it will come, due to pressure on services."

Prices and rents had skyrocketed since the Syrian influx began, and there was more competition for jobs. "We are looking to the international community to help us. We need long-term support. It will take at least five years to get them back even after the war has ended," he said.

Aoife McDonnell, of UNHCR, the UN's refugee agency, said that despite border closures and tightened security, increased numbers of refugees were also heading for Jordan from central and northern areas of Syria because of increased instability and insecurity in Lebanon and Iraq, particularly Anbar province, and because of heavy militarisation along the Turkish border. Another growing concern was malnutrition and disease.

"More and more refugees are reporting there is just no food to be had. And this is happening in Syria, which was bread basket of the region. Their physical appearance when they come in is very weak and deteriorating," she said.

An outbreak of polio inside Syria was also worrying. It had happened despite a UN-led, $39m multi-country vaccination campaign, aimed at 23 million children, and increased funding for related water and sanitation projects in Syria.

The international response to Syria has been almost unprecedented in cash terms, with the EU and member states such as Britain having committed a total of €2.6bn (£2.2bn) so far.

Zaatari camp alone costs $500,000 a day to run, according to ECHO. But it is clear much more is needed.

Joanna Wronecka, the EU ambassador to Jordan, said EU aid to the kingdom had doubled to €226m a year and was likely to double again. The US had also boosted assistance, including $1bn in new loan guarantees.

"Jordan needs more money and more help. They are planning economic reforms with the IMF and have agreed to end subsidies on food and bread and fuel, and are looking to implement it," Wronecka said. But such changes, she added, might contribute to rising inter-communal tensions in the short term.

Despite these problems, the manager of the UN's Zaatari camp, Kilian Kleinschmidt, said the independent, highly entrepreneurial, outlook of the Syrian refugees provided an encouraging pointer for the future.

After a period in 2012-13 when UN and NGO workers were "shit-scared" to enter parts of the camp, due to frequent riots, stonings, and gang attacks, the situation had been transformed with refugees empowered to take charge of their lives.

"All the people here have seen something horrible. They have been hiding and running, they have experienced killing and torture, spying and betrayal. These people don't trust anybody any more. Plus they are traditionally traders and smugglers. They are anti-government. They don't like authority," he said.

So rather than emphasising physical control and keeping resentful recipients dependent on food and other handouts, UN workers had begun distributing vouchers, which enabled the refugees to buy what they wanted. More cost-effective, direct cash assistance was now being extended by the use of ATM machines, backed by improved registration and refugee ID using iris recognition isometric technology, Kleinschmidt said.

"We now have 2,500 shops in the camp. We even have supermarkets," he said. "It costs $5,000 to open a shop at a prime location on the main street, which we call the Champs Élysées. We've put in better water and better roads. We've appointed street leaders and licensed 'electricity ministers'. Before they were stealing the electricity, now they are in charge of it."

Other key moves have included the expansion of the camp's school system, for boys and girls, using Jordanian and Syrian teachers, more employment opportunities for refugees, and the search for private-sector partnerships and investment.

Companies, including Google, and universities and colleges such as Massachusetts Institute of Technology, were interested in camp projects, he said. Uefa set up a football club and oversaw a tournament that attracted 500 children.

Unrest, exploitation, child labour and sexual violence in the camp had greatly declined, Kleinschmidt said. The sudden implosion of Syria's relatively sophisticated society had produced "the most shocking crisis in the world", he said.

But at Zaatari, at least, after the shattering dislocation and disintegration of the past three years, they were "retraining communities to look after each other". And the Syrians, he said, were retraining the UN agencies to carry out humanitarian assistance differently, and in a better way.

Among the more than 100,000 dead in the three years since the Syrian civil war began are at least 11,000 disappeared into the Assad regime's custody. But the true number may be much higher, the Guardian finds in interviews with released prisoners and relatives of the missing